Thickness is one of the quality control data of the protective barrier membrane which is required by the U.S. Government and American Society for Testing and Materials (ASTM). The minimum thickness requirement is 0.1 mm for rubber surgical gloves [2], and 0.08 mm for rubber examination gloves [3].
The thickness of rubber barrier can be tested using the following methods:
Micrometer method. A dial micrometer with an anvil and a pressure foot is used to exert a certain force on the membrane, which is placed between the anvil and the pressure foot. The dial is graduated to read the thickness of the membrane [4], [5].
Optical method. A microscope equipped with a mechanical stage, and a ruled glass disk or ocular micrometer is used to directly read the scale of the thickness of a barrier membrane, which stands edgewise on the stage [6].
Acoustic echo method. An acoustic system measures the thickness of a barrier by propagating an acoustic wave through the barrier membrane such that echo waves are generated and received by a transducer. The thickness value is obtained from the time lapse between the propagated wave and receipt of the echo wave [7].
Two U.S. patents deal with the acoustic echo method using a sweeping acoustic frequency and the echo waves from the interfaces either to measure the thickness of a coating layer on a substrate, or to control the depth of removal of a selected material on a polishing pad [8], [9]. The transmission pattern of the acoustic waves is provides a basis for determining the thickness of the coating or the depth of the removal.